This is something that I recently came across when we upgraded our office server and to be honest it had me stumped for a little while, but here is what I found.
Essentially we setup our new SBS 2011 Standard server using all of the MS consoles and wizards including the wizard to created the email address domain. After a few days I found that we could not send any outbound emails from devices that were using AirSync, these included Windows 7 Phones; iPhones; Windows Phones; iPads as well as a host of other devices that connect to Exchange using AirSync (formally ActiveSync). There is a great deal of information about this but all of it related to having an invalid character in the domain name. However, having checked through the setup there were not illegal characters in the domain name yet we continued to get the same error.
What I found was that when you setup an ‘Accepted Domain’ the wizard will ask for a name as part of the wizard. This has traditionally been a descriptive name however this is where the issue seems to lie. In our case, what I did was changed the name to be the same as the domain name and it now works correctly.
Hopefully this should help others.